In heavy vehicles such as fire engines, mobile cranes, special vehicles, heavy military vehicles, etc. it has hitherto been conventional practice to construct the suspension and the so-called terrain compensation for travelling over ground unevennesses using heavy leaf springs or leaf spring sets. It is advantageous in such a relatively simple suspension system that the longitudinal and transverse guidance of the axles is, so-to-speak, integrated free into the system. The heavy leaf spring sets are also able to absorb the often powerful rotary forces on the axle body occurring on braking and starting with a heavy vehicle.
However, disadvantages exist because such leaf spring sets are heavy, have a relatively small spring displacement and their elasticity decreases relatively rapidly. In addition, leaf spring systems cannot be switched over for the extreme operating conditions of empty weight on the one hand and heavy (maximum) loading on the other.
In addition, in the case of a leaf spring system neither a vertical adjustment of the vehicle, nor a slope compensation can be incorporated. The leaf spring elements require too much space on installation and reduce the obliquity of the wheels on the guided axles. Leaf spring systems also have a prejudicial effect on the headroom of a vehicle, i.e. the latter or the height of its loading surfaces necessarily become too high and this leads to serious disadvantages, such as the risk of tilting through the also high centre of gravity.
Attempts have been made to obviate these disadvantages by a number of measures, such as single wheel suspensions, etc. However, single wheel suspensions have proved unsuccessful for heavy vehicles, because very large forces occur on the wheels (force transmission and braking), which cannot easily be absorbed. Usually there is also not adequate space between the wheels, the axles and on the vehicle body to permit the fitting of such mechanisms with the necessary dimensions.